The invention relates to electric lamps and particularly to high pressure electric lamps. More particularly the invention is concerned with a seal structure and a method of sealing a high pressure electric lamp.
An electric lamp with a long life has been a constant goal since the time of Edison. One method is to use a larger filament, but that requires larger supports, envelope and so on. The whole structure becomes more expensive and may be less efficient. Another method is to use a high pressure fill gas that resists filament evaporation. Unfortunately, high pressure lamps can mechanically fail, and large high pressure lamps inherently contain more stored energy than small lamps. Large high press lamps are then seen to be dangerous and uneconomical. On the other hand small, high pressure lamps, while potentially economical, can be difficult to accurately construct and fill to a proper pressure due to small irregularities in their construction. These variations in pressure result in lamps with unreliable life spans. The typical method of filling a high pressure lamp requires filling and purging the lamp one or more times to remove fouling materials from the lamp. To do this through a small exhaust tube is time consuming, and does not necessarily yield a consistently clean lamp. There is a need for a method to fill high pressure lamps without using an exhaust tube. The exhaust tube process is slow because it requires filling to be completed at a first station before sealing of the tubulation is started at a second station. There is also a need for a filling process wherein the lamp is filled and the bulb are sealed simultaneously.
Freezing out fill materials, while sealing the exhaust tubulation is a known process. Freezing out the fill material to enable the sealing process is costly, and along with the necessary fill material, tends to freeze out materials that can foul the lamp. Dirty lamps tend to have shorter lives than clean lamps.
Long life, efficient incandescent lamps can be produced by using a high-pressure fill gas, such as xenon, to inhibit tungsten evaporation at higher coil temperatures. Products of this type are being considered for use as automotive turn signal lamps. A second desired feature for signal lamps is compact size that to then reduce the reflector and lens size needed for the optical system. Reducing the typical seal geometry along with precisely placing the filament would enable for a more compact lamp, and lamp system.
Philips NV has introduced a high pressure, compact light source for automobile turn signal applications. The technology, materials and processes involved in making the lamp are described in international patents WO 98/50942 and WO 98/50943. In this product, a sintered glass wafer is used a platform to mount a filament. The sintered glass wafer is stable during sealing and it occupies less space than a conventional mount or press seal. The sintered glass wafer requires a solder glass seal formed between the bulb and sintered glass wafer. The wafer is comprised of powdered and pressed P-360 glass that is sintered with two lead wires and a metal exhaust tube to form a hermetic component. After coil mounting, the sintered glass mount and bulb are joined by a solder glass in an inert or reducing atmosphere, to protect the filament. The bulb and mount assembly is then placed in a vessel that is attached to a vacuum and filling system. The lamp is xe2x80x9ccleanedxe2x80x9d or outgased and the vessel, including the internal volume of the lamp, is filled with high-pressure xenon (3 to 8 bar). This filling method is said to be cleaner than the common method of high pressure filling of lamps using liquid nitrogen to freeze out a fill gas. Laser welding the metal exhaust tube then tips off the lamp, while the vessel is under pressure. Alternatively, an electric arc or plasma weld is suggested as a tipping processes.
The tubulated lamp with a freeze out process has several disadvantages. The metal exhaust tube is expensive, and the frit glass wafer is more difficult to make than a typical glass mount. The solder glass seal process is a time consuming operation and requires large equipment for high rates of production. The overall result is a relatively expensive lamp that meets the criteria of long life and compact design.
A high pressure lamp may be made by providing a high pressure vessel; locating an electric induction energy source near the vessel; and locating in the vessel a lamp capsule having a wall defining an enclosed volume and an opening. The high pressure vessel is then filled so that the enclosed volume is filled with a fill material. A melt fusible wafer is located adjacent the opening with the wafer spanning the opening. The wafer is pressed by an electric induction heatable energy receiver against the wafer. By supplying sufficient electric power to the induction energy source to induce heating of the receiver, the portion of the wafer may be melted, fusing the wafer to the capsule along the opening thereby sealing the capsule.